1. Field of the Invention
The invention refers to a marking device using a laser for the creation of an optical mark or a similar kind of projection onto an object.
2. Description of Related Art
Marking devices are known and a positioning device for one such marking device may have two deviation mirrors, placed within the beam path of the laser beam. These mirrors are movably placed in a relative position to the laser and can be brought into different swiveling positions around a neutral position by a galvanometer. For a two-dimensional alignment of the laser beam onto the different parts of the surface of an object to be marked, swiveling axes of the deviation mirrors are placed across each other.
For the creation of a two-dimensional optical projection onto an object, the laser beam is directed in quick succession to the different parts of the object which lie within that part of the object""s surface that is to be marked, e.g., by moving the laser beam corresponding to a scanner movement along the surface of a line or a polygon sequence. The scanning frequency of the deviation mirrors is chosen in a way that the viewer is not able to realize the movement of the laser point which is created at the laser point""s point of impact on the object surface, and the human eye, because of its inertness, will get the impression of a two-dimensional image.
The marking device has proved its worth especially for users who have to optically mark on a working tablexe2x80x94or something similarxe2x80x94several different parts one after the other. It is, for example, usual to optically mark at the working table of, for example, a milling machine, or a saw, those parts one after the other on which you want to place stretching elements for the fixing of a work piece. That will make it easier for the operator to position the stretching elements on the working table. If necessary, it is also possible to project with this device additionally a contour line onto the work piece. This line makes it easy to find the exact position into which the work piece has to be brought on the working table.
However, the marking device has one disadvantage. That is, the projections only have a relatively low brightness and therefore are not well visible in bright and artificially lightened rooms. Although there are marking devices which show an extended brightness of the projection because they use lasers with a much higher beam power, these marking devices have one disadvantage with respect to the formerly mentioned ones. They do not fulfill the criteria for being classified as laser class 3A according to the norm DIN EN60825-1:1997 and the corresponding international norm. According to these standards the average power density of the light, referring to a 7-mm aperture, is not to exceed a given limit. According to the safety requirements of this norm, a laser safety officer responsible for the marking device has to be appointed. But very often a safety officer with such a qualification is not available.
A device is needed to create a marking device as mentioned first which can be classified as laser class 3A but which still produces a bright projection.
The solution for this problem is, firstly, that the marking device has a feature for speed acquisition, with which the positioning speed of the laser beam can be recorded and secondly, that the power supply unit has a control unit, connected to this speed acquisition device. This control unit should switch off the laser beam in case the positioning speed of the laser beam falls below a minimum speed and/or reduces the beam power of the laser if the positioning speed of the laser beam decreases.
The invention is based on the fact that the power density of the lighting, which is an average 7-mm aperture for the classification into laser class 3A, increases if the scanning or positioning speed of the laser beam is reduced and the power density decreases if the scanning and positioning speed is raised. This means that the average power density at the 7-mm aperture is at its peak if the laser beam is not moving and meets the 7-mm aperture completely with its beam cross section. This may happen especially in the turning points of the laser beam""s scanning process. The concept of the invention provides a reduction of the classification into laser class 3A problematic average power density, so that the laser beam is switched off if it falls below a given minimum scanning speed or that its beam power is at least reduced. It is therefore also possible for a beam speed which is higher or equal to the minimum scanning speed, in spite of a classifying of the marking device into laser class 3A, to operate the laser with a comparatively high beam power to make a bright projection possible. As a result, it is not necessary to appoint a laser safety officer even though a bright laser is being used. If the beam speed falls from an initial value, the beam power of the laser is reduced, which means the laser beam remains switched on but with a reduced power. As a result, a bright projection is possible, even with a low beam speed or if the laser beam is not moving, because the human eye cannot discern between a high speed, low power laser beam and a low speed, high power laser beam.
In one embodiment of the invention, the positioning device has at least a deflector which is placed in the beam path of the laser beam and which is movable relative to the laser by a positioning mechanism.
In another embodiment, the speed acquisition device is able to determine an angular speed of the deflecting element. The deflecting element can be a galvanometer mirror. This guarantees a compact and relatively inexpensive mounting of the positioning device and also permits a high positioning speed of the laser beam. The positioning device may have two deflecting elements, placed behind each other in the beam path, which are movable around two cross axes, in particular, two rectangular axes, to make a two-dimensional projection possible. It is also possible to achieve a two-dimensional projection with a single deflecting element which is movable in two directions. The positioning device may be placed to guarantee that people maintain a correct safety distance from the deflecting element(s). The positioning device may, for example, be mounted at a certain height from the building""s ceiling.
In yet another embodiment, a safety zone exists with a given safety distance value in the radiation area of the laser while the marking device has a detector to detect people in the safety zone. The detector is connected to a shutoff device for the laser. If, for a positioning device with one or more movable beam deviation elements, the positioning speed of a laser point which is projected onto an object by the laser beam is inversely proportional to the distance of the object from the point where the laser beam meets the deviation element, then this guarantees that people will keep to the required safety distance while the laser is operating. The laser beam power can then be chosen in a way that the average power density of the laser beam, referring to a 7-mm aperture and for that given safety distance, will still lie within the range that makes it possible to classify the marking device into laser class 3A. The safety zone may, for example, be surrounded by a removable protecting grid, behind which the positioning device and/or the laser are placed. An electronic switch can be used as a detector which will release the laser when the protection grid is closed and block it when the grid is open. The shutoff device is preferably there to stop the power supply of the laser. The switching off device may also have a beam interrupter or some similar device which will preferably be placed in the beam path of the laser between the laser and the positioning device.
The detector may have at least a non-contact proximity sensor able to function as a movement detector. This eliminates the need for a protection grid or a similar costly and complicated device surrounding the safety zone. The movement detector can be equipped as an ultrared and/or an ultrasonic movement detector.
The device in accordance with the subject invention may have a shutoff device with a storage for a release signal. The storage may have one entry connected to a release switch or a similar release device to activate the release signal and another entry connected to the detector to cancel the release signal when it detects a person within the safety zone. The control device is adjusted in such a way that the laser beam can only be activated when the release signal is set. After a person has been detected in the safety zone, the laser beam stays switched off until it is released again manually with the release device. This provides additional protection for preventing damage to the human eye through laser radiation.
The control device should be arranged in a way that the laser beam will have a first beam power value for the first positioning speed and a second value for a second positioning speed such that the beam power will increase linearly with the positioning speed within the speed range between these two positioning speeds. By doing so, a more or less constant brightness of the projection or the projected marking can be reached independent from the deviation speed of the laser beam. The control device may be arranged in a way that the laser has a low beam power when the laser beam is not moving, and the beam power, with increasing positioning speed of the laser beam, is raised until the maximum power of the laser is reached.
Using a relatively simple speed acquisition device, the positioning speed of the laser beam may be determined from a speed controlling signal which is used to control the positioning device. It is assumed that the actual positioning speed of the laser beam is nearly identical with the speed controlling signal.
In yet another embodiment of the invention, the speed acquisition device is arranged as a measurement device and has a sensor which measures the current consumption of the positioning power mechanism and by that indirectly measures the positioning speed of the laser beam. The actual positioning speed of the laser beam can be measured by this method in a very easy way.